IMPACT OF AFRICAN YAM BEAN PRE-SOAKING DURATION ON COOKING TIME AND COMBINED EFFECT OF PRE-SOAKING AND BLANCHING ON NUTRIENTS AND ANTI-NUTRIENTS IN THE FLOURS

Black variety of African yam bean (Sphenostylis stenocarpa) were pre-soaked in 5% solution of unripe plantain peel ash (1:3w/v) for 6, 12, 18 and 24 hr and the effect of soaking duration on the cooking time investigated. Also, investigated was the combined effect of pre-soaking (6, 12, 18 and 24 hr) and blanching (100°C for 15 min) the yam beans on the nutrients and anti-nutrient contents in the flours. Flour from un-soaked but blanched yam bean served as the control sample. Result showed that the cooking time of yam bean seeds decreased from 130 min for un-soaked seeds to 40 min for 24 hr pre-soaked seeds. Percentage reduction in cooking time ranged from 44.62% for 6 hr pre-soaked seeds to 69.23% for 24 hr pre-soaked seeds. Flours prepared from un-soaked seeds had significantly (P = .05) higher crude protein, HCN, oxalate, phytate and tannin and insignificantly (P = .05) higher crude lipid and crude fibre contents than the flours from pre-soaked seeds. The aforementioned constituents consistently decreased with longer soaking time. Percentage reduction of HCN, oxalate, phytate and tannin ranged from 34.44, 17.59, 24.08 and 25.73% for flours prepared from seeds that were pre-soaked for 6 hr to 85.38, 56.96, 69.25 and 65.22% for flours from seeds that were pre-soaked for 24 hr. On the contrary, flours prepared from the un-soaked but blanched seeds had lower contents of ash, carbohydrate, K, Na, Ca, Mg, Fe, Zn, and energy value than flours from seeds that were pre-soaked in solution of unripe plantain peel ash before blanching. The aforementioned constituents consistently increased with the longer soaking time. Reduction in oxalate, phytate and tannin in the flours as a result of pre-treatment effect would enhance the bioavailability of mineral elements like calcium, magnesium, iron and zinc that usually form complexes with these anti-nutrients.